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Birder's Journal: This Warbler Is a Master of Deception |
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Robert Winkler for National Geographic News |
| August 29, 2002 |
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A favorite trail of mine runs for five miles along the west side of the largest reservoir in the county. I suppose I've hiked sections of it a thousand times, but the odd sensation that brought my gaze to my feet one summer afternoon was something new. A worm-eating warbler had flapped across my path, grazing my boot with its wings. Now it was fluttering along the forest floor and chipping nervously, behavior that meant it probably had a nest nearby. Worm-eating warblers nest on the ground, and they defend their eggs or young by trying to lure predators away. Although tempted to search for the nest, I gave the area only a cursory look. Even with a good clue like this, nest-finding requires patience. I wanted to get back into the rhythm of walking, and let the warbler, probably an incubating female, get back to her eggs. Returning along this stretch of trail a half-hour later, I had forgotten the warbler, until she cut me off again. She squeezed under my right boot just before it hit the ground. This time, I concentrated on where she first appeared and found the nest almost immediately. It was tucked into the side of a leafy knoll, just two feet off the trail. Next to a rock, and overhung with a shelf of fallen leaves, the nest contained four tiny whitish eggs flecked with brown. Although I had never found a worm-eating warbler nest, I quickly moved on. Every second I lingered exposed the eggs to danger and kept the female from incubating. I had not touched the nest. It would have been a death sentence for the eggs, because the scent of a human, often leading to food, attracts predators. Even my innocent pause put a worrisome glitch in my scent trail. Hours later, a rapacious raccoon foraging in the darkness might know I had stopped. Its suspicions raised, it could start sniffing around and find the nest. As I headed back to the car, I wondered how worm-eating warblers survive when they build their nest on the ground, so vulnerable to predators. Walking the same trail a few days later, I had trouble finding the nest, though I had made careful note of nearby landmarks. But I was still looking for the whitish eggs. Soon I realized that where the eggs had been, there were now four nestlings. Covered in brownish-gray down, they blended into the shadow of the overhanging leaves. The baby birds huddled together, quiet and motionless. The mother flew off as usual but seemed no more agitated than she had been when guarding the eggs. I kept this visit even briefer than the first. More than a week had passed by the time I checked the warblers again. The nest was empty and intact, and I was relieved to find no signs of disaster: blood, feathers, or other remains. Surely a raiding raccoon would have dislodged the fine grasslike stems resting on the nest's front rim. One thing did bother me: the silence. If the nestlings fledged, where had they gone? A few minutes' walk from the nest, just as I was accepting the worst, I flushed a juvenile worm-eating warbler from the side of the trail. Flapping furiously but moving slowly, it rose into the air and made a precarious landing in a sapling a few feet away. An adult then flew in quickly and gracefully, chipping at me in anger. Stubby-tailed and plump-looking, the young bird was mostly pale yellow, its crown showing just a hint of the bold dark stripes that distinguish the adult. Consistent with my noninterference policy, I kept going. On my return, I saw two young birds and an adult. Unlike the open deciduous woods around the nest, this rocky slope offered plenty of cover. If danger approached, the awkward-flying young had mountain laurel thickets and a spattering of hemlocks in which to hide. I can't prove these warblers were from the nest I had found, but I believe they were. The young were the right age, and on subsequent walks I would see a family of three or more worm-eating warblers within 100 yards of the nest. They were lucky birds, I thought, but on reflection I realized this was underestimating them. Like the thief in Edgar Allan Poe's Purloined Letter, the adult female I had almost stepped on was a master of the art of deception. She had placed her well-camouflaged nest "immediately beneath the nose of the whole world, by way of best preventing any portion of that world from perceiving it"—a survival strategy that protected her eggs through 13 days of incubation, and her nestlings until they fledged 10 days later. Robert Winkler's book of essays on his adventures with birds of the "suburban wilderness" will be published in 2003 by National Geographic Books. 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